System and method for unscheduled wireless communication with a medical device

ABSTRACT

Data is communicated from a transmitter of an external unit to a receiver of an implantable medical device. The receiver of the implantable medical device operates in a wide band receiver mode to detect the transmission from the external unit and operates in a narrow band receiver mode to receive the data.

CROSS-REFERENCE TO RELATED APPLICATIONS

Reference is made to the following applications filed on even date: [Attorney Docket No. P22283] “SYSTEM AND METHOD FOR UNSCHEDULED WIRELESS COMMUNICATION WITH A MEDICAL DEVICE” by Gregory J. Haubrich; Len D. Twetan; David Peichel; Charles H. Dudding; George C. Rosar; and Quentin S. Denzene [Attorney Docket No. P23271] “COMMUNICATION SYSTEM AND METHOD WITH PREAMBLE ENCODING FOR AN IMPLANTABLE DEVICE” by Gregory J. Haubrich, Javaid Masoud, George C. Rosar, Glenn Spital, and Quentin S. Denzene; and [Attorney Docket No. P23054] “IMPLANTABLE MEDICAL DEVICE COMMUNICATION SYSTEM WITH MACRO AND MICRO SAMPLING INTERVALS” by Glenn Spital.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to implantable medical devices. More specifically, the present invention relates to implantable medical devices with communication systems.

2. Description of the Related Art

Implantable medical devices (IMDs) are now used to provide countless therapies and to monitor a wide variety of physiological events. Conventionally, communication with IMDs has been with inductive coupling communication systems. Such systems, however, are generally only capable of communicating over very short distances. As a result, a magnetic head of a programmer (or other external device) must be located very near the IMD for communication to occur. More recently, radio frequency (RF) communication systems have been developed for use with IMDs. RF communication provides a number of benefits over inductive coupling communication systems, including much greater communication distances.

Because an IMD is implanted within the body of a patient, battery usage is one consideration for an IMD communication system. Methods of reducing the amount of time that the receiver of an IMD operates can be beneficial in improving power consumption.

BRIEF SUMMARY OF THE INVENTION

Data is communicated in a transmission between an external unit and an implantable medical device having a receiver that operates in a wide band receiver mode and a narrow band receiver mode. In the wide band receiver mode, the receiver detects a transmission on any one of multiple communication channels. In the narrow band receiver mode, the receiver receives the data from one communication channel.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram illustrating a communication system for communicating data between an implantable medical device (IMD) and an external unit.

FIG. 2 is a block diagram illustrating the components of the IMD and the external unit that make up the communication system.

FIG. 3 is a graphical illustration of a transmission bit stream including an encoded preamble and data.

FIG. 4 is a graphical illustration of pulse width encoding.

FIG. 5 is a graphical illustration of channel data embedded in the preamble with pulse width encoding.

FIG. 6 is a table illustrating frequency shift encoding.

FIG. 7 is a graphical illustration of communication mode data embedded in the preamble with frequency shift encoding.

FIG. 8 is a block diagram of a receiver of the IMD.

FIG. 9 is a flow chart illustrating a method of operating the receiver.

FIG. 10 is a timing diagram illustrating an alternate method of operating the receiver.

DETAILED DESCRIPTION

FIG. 1 is a schematic diagram illustrating communication system 10 that enables communication between IMD 12, and external unit 18. In one embodiment, IMD 12 is an implantable cardioverter defibrillator (ICD), but the present invention is equally applicable to many types of medical devices, including both implantable medical devices and external medical devices. IMD 12 is capable of providing therapies and/or sensing physiological events of the heart of patient P via lead 14. Antenna 16 is used to communicate with external unit 18 and may be any device capable of sending or receiving electromagnetic energy, including, for example, a surface mounted antenna, an inductor, or a half-wave strip.

External unit 18 is a device, such as a medical device programmer, capable of communication with IMD 12 via antenna 20. External unit 18 includes antenna 20, which may be any type of RF antenna capable of communicating in the desired RF frequencies with IMD 12, and may be located inside or outside of a housing of external unit 18.

FIG. 2 is a block diagram illustrating some of the components of IMD 12 and external unit 18 that make up communication system 10. External unit 18 includes antenna 20, external unit circuitry 27, and transceiver 28. Antenna 20 is coupled to transceiver 28 of external unit 18. External unit circuitry 27 includes a microcomputer and software to control the operation of external unit 18. Transceiver 28 enables external unit circuitry 27 to transmit and receive communications with IMD 12. Transceiver 28 of external unit 18 includes transmitter 32 and receiver 34.

IMD circuitry 29 includes a microprocessor for controlling the operation of IMD 12 and for processing data, therapy delivery circuitry for delivering a therapy through lead 14, and sensors for generating data, including data generated by detecting electrical signals on lead 14. Transceiver 30, coupled to antenna 16, enables IMD circuitry 29 to transmit and receive communications with external unit 18. Transceiver 30 includes transmitter 36 and receiver 38, which transmit and receive data using RF electromagnetic waves.

Communication between IMD 12 and external unit 18 can be performed over any communication band. In one embodiment, the communication occurs over a public radio frequency band. In another embodiment, the communication occurs over the Medical Implant Communication (MICs) band between 402 MHz and 405 MHz. Although the present invention is described with reference to radio frequency bands, it is recognized that the present invention is also useful with other types of electromagnetic communication.

Because IMD 12 has a finite battery capacity, one consideration in the design of RF communication system 10 is the energy efficiency of IMD 12. One factor in the energy efficiency of IMD 12 is the time transceiver 30 is engaged in actively transmitting or receiving. Thus, an improvement in energy efficiency of transceiver 30 will lead to increased battery life of IMD 12. Energy efficiency is less of an issue in the design of external unit 18, because external unit 18 is generally connected to an external power source such as a 120V AC. Therefore, reducing the energy consumption of transceiver 30, even in exchange for additional energy consumption of transceiver 28, is beneficial.

While transmitters only need to be turned on when there is something to transmit, receivers are turned on much more frequently. No communication can take place unless the receiver is on, at least momentarily, to detect an attempted transmission. To provide a fast response time, a receiver may sample a communication channel as often as twice every second or more; but, a receiver that turns on just twice every second will turn on 172,800 times in one day. A transmitter, on the other hand, may turn on only a handful of times in that same period. Therefore, an increase in the energy efficiency of a receiver can provide an increase in the effective life of the power supply.

Returning to communication system 10 of FIG. 2, transmitter 32 transmits a preamble signal prior to the transmission of data. Receiver 38 samples the communication channels periodically for this preamble signal, rather than remaining on at all times, while still ensuring that receiver 38 will not miss the transmission of any data. The preamble signal contains a modulation pattern recognizable by receiver 38. If receiver 38 detects signals on a communication band, but finds that the signals do not contain the modulation pattern, receiver 38 can shut down since the detected signal is not a communication initiated by transmitter 32 for receiver 38. Furthermore, the preamble signal contains embedded data that allows the receiver 38 to further improve efficiency. This data provides link-pertinent information (such as receiver channel and communication mode) for the subsequent transmission of data. Receiver 38 may continue operating in a low power receiver mode while receiving the embedded data, and then adjust its receiver configuration settings as specified by the embedded data to initiate the higher power receiver mode for receipt of the transmitted data.

Receiver 38 of IMD 12 (described in more detail below with reference to FIGS. 8-9) operates in a low-power, wide band receiver mode that can simultaneously sample for energy on multiple communication channels, and a narrow band receiver mode for communication on a single channel.

FIG. 3 is a graphical illustration of a transmission bit stream 40 transmitted by transmitter 32. Transmission bit stream 40 includes preamble signal 42 and data 48. In one embodiment, preamble signal 42 has a duration greater than or equal to a fixed duration, referred to as the macro sampling interval. By transmitting preamble signal 42 for greater duration than the macro sampling interval, receiver 38 can periodically sample received energy for a communication, but turn off between samples. The off-time of receiver 38 conserves energy as compared to having receiver 38 on continuously.

Preamble signal 42 includes wake up segment 44 and ready segment 46. To ensure its detected by receiver 38, wake up segment 44 is the segment that first informs receiver 38 that transmitter 32 is attempting to communicate. Wake up segment 44 is transmitted for a duration greater than the macro sampling interval of receiver 38. Wake up segment 44 includes sync pattern 50 that informs receiver 38 that data 48 is about to be transmitted and embedded channel data 52 that informs receiver 38 on which channel that data is to be transmitted.

Sync pattern 50 is a repeating pattern of bits. In one embodiment, sync pattern 50 is a transmission of alternating on-off keyed (OOK) 0 and 1 bits, each bit having a duration of about 50 microseconds to create a series of repetitive pulses having about 50 microsecond on-time and about 50 microsecond off-time. This transmission results in a transmitted tone having a frequency of about 10 kHz. One of the benefits of OOK sync pattern 50 is that receiver 38 can be designed with a very simple, low-powered OOK or AM receiver capable of detecting the transmission and validating the modulation of the transmission. If energy is detected that does not contain this modulation pattern, receiver 38 can quickly identify the energy as something other than the desired transmission and shut down to conserve energy. Sync pattern may include any recognizable pattern of bits, at any desired bit frequency. Other types of modulation could also be used to validate the modulation pattern, such as amplitude modulation (AM) or vestigial sideband modulation (VSB), phase shift keying (PSK), frequency shift keying (FSK), etc.

During transmission of wake up segment 44, transmitter 32 alternates between transmission of sync pattern 50 and channel data 52. However, channel data 52 is encoded within sync pattern 50 in such a way that the detection and validation components of receiver 38 do not notice the embedded data. In one embodiment, receiver 38 includes a transition detector that detects the leading edges of sync pattern 50, and channel data 52 is embedded in such a way that the leading edges continue in the same pattern as sync pattern 50, but the falling edges are adjusted to encode data. In other words, the pulse width of sync pattern 50 is modified to embed channel data 52 within wake up segment 44. Channel data 52 is described in more detail with reference to FIGS. 4-5 below.

Following wake up segment 44, transmitter 32 transmits ready segment 46 that informs receiver 38 that transmission of data 48 is about to take place and also provides additional encoded configuration data. Ready segment 46 includes sync pattern 50 and mode data 54. In one embodiment, sync pattern 50 of ready segment 46 is phase shifted 180 degrees from sync pattern 50 of wake up segment 44, such that receiver 38 can differentiate between wake up segment 44 and ready segment 46. In an alternate embodiment, receiver 38 differentiates between wake up segment 44 and ready segment 46 by detecting encoded mode data 54 within ready segment 46. Sync pattern 50 of ready segment 46 can be any other distinct pattern of bits which can be distinguished from sync 50 of wake up segment 44.

Ready segment 46 is transmitted for a period of time greater than a micro sampling interval of receiver 38. After receiver 38 has detected and validated wake up segment 44, and decoded channel data 52, receiver 38 resumes sampling, but now at a shorter interval, referred to as the micro sampling interval. Because ready segment 46 has a greater duration than the micro sampling interval, receiver 38 will detect ready segment 46 prior to the transmission of data 48 from transmitter 32, while still conserving power until detection of ready segment 46.

Embedded within ready segment 46 is encoded mode data 54, which provides receiver operating mode data to receiver 38. This data may include link pertinent information such as desired data rate and/or telemetry protocol for the transmission and reception of data 48. In one embodiment, mode data 54 is embedded within ready segment 46 using frequency shift encoding. Similar to phase shift encoding described above, frequency shift encoding maintains the OOK packet structure of sync pattern 50 to enable receiver 38 to continue detecting and validating the modulation pattern of preamble 42. However, rather than adjusting the pulse width of sync 50, frequency shift encoding adjusts the transmission frequency slightly to encode mode data 54. Frequency shift encoding is further described with reference to FIGS. 6-7.

After transmitter 32 has completed the transmission of preamble 42, data 48 is transmitted. Data 48 may include pure data, messages, requests for a response, and/or any other desired communication between transmitter 32 and receiver 38. All types of data 48 are referred to generally as data.

FIG. 4 is a graphical illustration of one embodiment of a pulse width encoding scheme to encode data within wake up segment 44. Pulse width codes include sync pattern 50, zero pattern 56, and one pattern 58. Sync pattern 50, as previously described, is a repeating pattern of OOK 0 and 1 bits. Each box of FIG. 4 represents one half of a bit length, where a shaded box represents a transmission and an unshaded box represents no transmission. In one embodiment, each bit of sync pattern 50 is 50 microseconds long, such that each box of FIG. 4 represents 25 microseconds.

Pulse width encoding enables data to be encoded within wake up segment 44 without affecting the timing of the leading edges of the bits of the transmission and also maintaining an overall 50% duty cycle. Maintaining a consistent timing of the leading edges allows receiver 38 to verify that the transmitted signal conforms to the appropriate modulation. By adjusting only the trailing edge of the bits, the leading edges remain unchanged.

Zero pattern 56 includes two pulses. Each of the pulses has a leading edge that is equivalent to the leading edge of sync pattern 50. The first pulse has a duration of one-half of a sync bits, and the second pulse has a duration of one and a half of a sync bit. Although the width of the pulses have been varied, the overall duty cycle of zero pattern 56 remains 50%.

One pattern 58 also includes two pulses, with each pulse having a leading edge that is equivalent to the leading edge of sync pattern 50. The first pulse has a duration of one and a half of a sync bit, and the second pulse has a duration of one-half of a sync bit. One pattern 58 also has an overall duty cycle of 50%.

FIG. 5 is a graphical illustration of channel data encoded with pulse width encoding on a portion of wake up segment 44. The portion of wake up segment 44 shown includes sync pattern 50 (repeated once), five bits of encoded channel data 52, followed by another sync pattern 50 (repeated once). Periodically between transmissions of sync pattern 50, channel data 52 is transmitted.

Channel data 52 allows receiver 38 to sample all channels of a communication band at once with a low power wide band receiver. Once energy has been detected, receiver 38 decodes the communication channel from channel data 52 and adjusts receiver 38 to the appropriate channel. In this way, receiver 38 is able to conserve energy by determining the appropriate communication channel without having to scan each channel individually.

In the embodiment illustrated in FIG. 5, channel data 52 is binary data having five bits. FIG. 5 also shows pulse width encoded channel data of the binary code for channel 1 (00001) transmitted between sync patterns 50. Additional link pertinent information (e.g. data rate, channel, device ID, etc.) could also be transmitted to receiver 38 using the same pulse width encoding technique, if desired. Channel data 52 is repeated periodically within wake up segment 44.

After receiver 38 has received channel data 52 and has adjusted to the appropriate communication channel, it next monitors for ready segment 46 containing mode data 54. Ready segment 46, consists of sync pattern 50 and encoded mode data 54. As described above, in one embodiment, sync pattern 50 of ready segment 46 is shifted 180 degrees from sync, pattern 50 of wake up segment 44.

FIG. 6 is a table illustrating frequency shift encoding of ready segment 46. With receiver 38 adjusted to receive the appropriate communication channel, mode data 54 is communicated to receiver 38 through frequency shift encoding of sync pattern 50. Sync pattern 50, is transmitted at center frequency (fo) of the communication channel. By adjusting this frequency up or down, data can be encoded on ready segment 46, while still maintaining the (phase shifted) leading edges and modulation of sync pattern 50. In one embodiment, data is encoded by shifting sync pattern 50 up or down 100 kHz from center frequency (fo). To transmit a binary zero bit, sync pattern 50 is shifted down 100 kHz from center frequency (fo). This frequency is referred to as low frequency (fL), and is represented graphically by a downward pointing arrow. To transmit a binary one bit, sync pattern 50 is shifted up 100 kHz from center frequency (fo). This frequency is referred to as high frequency (fH), and is represented graphically by an upward pointing arrow.

FIG. 7 is a graphical illustration of a portion of ready segment 46 including frequency shift encoded mode data 54. This portion of ready segment 46 begins with phase shifted sync pattern 50. After sync pattern 50, mode data 54 is encoded within ready segment 46 by shifting the pattern of sync pattern 50 up or down in frequency. Any binary data of any length can be encoded within ready segment 46 using this frequency shift encoding technique. Mode data 54 can be transmitted once or repeated periodically within ready segment 46. In one embodiment, mode data 54 instructs receiver 38 of the appropriate telemetry protocol to use in receiving of data 48 from transmitter 32.

Now that transmitter 32 and transmission bit stream 40 have been described, the design and operation of receiver 38 of IMD 12 will be described.

FIG. 8 is a block diagram of one embodiment of receiver 38 of IMD 12 capable of receiving and processing preamble signal 42. Receiver 38 includes OOK (or AM) receiver 70, voltage controlled oscillator (VCO) 72, adjustable filter 74, threshold detector 76, digital to analog converter (DAC) 78, transition detector 80, phase locked loop (PLL) 82, RC oscillator 84, timer 86, and control circuitry 88.

OOK receiver 70 is a wide band receiver capable of receiving more than one channel at a time, such as a super regenerative receiver, which requires very low power consumption but provides very high sensitivity. One example of a super regenerative receiver is described in U.S. Pat. No. 4,786,903 by Grindahl et al.

In one embodiment, OOK receiver 70 is an adjustable receiver capable of being adjusted between a wide band mode capable of simultaneously receiving signals on all channels of a communication band and a narrow band mode capable of receiving signals on only a single channel of the communication band. In another embodiment, OOK receiver 70 is a wide band receiver that is operated in parallel with a narrow band receiver such that either or both receivers can be operated at any one time. Receiver 70 can also be another type of receiver, such as an amplitude modulation (AM) receiver. VCO 72 supplies a reference frequency to OOK receiver 70 to tune it to the appropriate receiver frequency.

Following OOK receiver 70 is adjustable filter 74, which is an adjustable low-pass filter used to filter out signals having undesired frequencies. Threshold detector 76, following adjustable filter 74, determines whether the amplitude of the received signal exceeds a threshold amplitude. A reference threshold amplitude is fed into threshold detector by DAC 78. Transition detector 80 follows threshold detector 76 and detects the leading edges of a received signal. Connected to transition detector 80 is PLL tone decoder or correlator 82, which determines how well an input signal correlates with an expected signal and generates a signal to adjust VCO 72 as needed.

RC oscillator 84 provides the time base for receiver 38. RC Oscillator 84 and timer 86 work in conjunction to provide appropriate timing signals to logic and state machines within control circuitry 88. Control circuitry 88, which controls the operation of receiver 38, may also include a microprocessor. Control circuitry 88 controls VCO 72, OOK receiver 70, adjustable filter 74, and DAC 78, and receives inputs from various components to enable it to monitor and control the operation of receiver 38. Control circuitry 88 also interfaces with IMD circuitry 29 of IMD 12.

FIG. 9 is a flow chart illustrating a method of operating receiver 38, begins by sampling the communication band at each macro sampling interval to detect whether the energy present within the communication band exceeds a threshold amplitude (step 90). In this step, receiver 38 operates in a wide band receiver mode to monitor all channels of the communication band at once. Receiver 38 turns on for only as long as needed to determine whether any energy present on the communication band exceeds the threshold amplitude. If no energy is present, receiver 38 turns back off until its next sample at the macro sampling interval.

Once sufficient energy is detected in the communication band, receiver 38 stays on verify whether the detected energy contains the modulation characteristic of preamble signal 42 of transmission bit stream 40 (step 92). To do so, receiver 38 monitors the low-to-high transitions to determine whether the transitions occur at the appropriate rate. For example, if wake up segment 42 is known to contain a 10 kHz bit pattern, receiver 38 monitors the energy to verify whether it corresponds to a 10 kHz pattern. If it does not, then receiver 38 identifies the energy as not being transmission bit stream 40 and turns off until its next sample. If energy is detected that exceeds the threshold amplitude and contains the appropriate modulation, receiver 38 then proceeds on the assumption that the energy present in the communication band is transmission bit stream 40.

After verifying modulation (step 92), receiver 38 remains on to monitor for encoded channel information (step 94) within wake up segment 44. As described above, channel data 52 is encoded within wake up segment 44 with pulse width encoding. Receiver 38 detects the pulse width encoding by monitoring for a series of uncorrelated bits (bits having a different pulse width than sync pattern 50). The uncorrelated bits are identified as channel data 52 and decoded by receiver 38. Decoded channel data 52 informs receiver 38 of the channel in which transmission bit stream 40 is being broadcast by transmitter 32.

Knowing the appropriate channel, receiver 38 adjusts to that communication channel (step 96). At the same time, receiver 38 is adjusted from the wide band receiver mode to a narrow band receiver mode in which only the single channel identified by decoded channel data 52 is received.

Following the adjustment to the appropriate channel, receiver 38 continues to monitor the channel for ready segment 46 (step 98). Since wake up segment 44 is longer than the macro sampling interval of receiver 38, transmission of wake up segment 44 will generally not be complete by the time that receiver 38 has adjusted to the appropriate channel. If no further data is needed from wake up segment 44, receiver 38 has no need to continue receiving the rest of wake up segment 44. Accordingly, receiver 38 turns itself off for short periods of time but periodically turns back on to sample wake up segment 44. The interval of time between samples when looking for ready segment 46 is referred to as the micro sampling interval, which is a period of time less than the duration of ready segment 46.

During each micro sample, receiver 38 determines whether wake up segment 44 is still being transmitted or whether transmission of ready segment 46 has begun (step 98). If wake up segment 44 is still being transmitted, receiver 38 turns off and resumes micro sampling until receiver 38 detects ready segment 46. Detection of ready segment 46 may be, for example, by detecting a phase change or a frequency change.

Once ready segment 46 has been detected, receiver 38 stays on to monitor ready segment 46 for encoded mode data 54. As described above, mode data 54 is encoded with frequency shift encoding. Receiver 38 detects mode data 54 by monitoring for a frequency shift in sync pattern 50, either up or down from center frequency (fo). When mode data 54 is detected it is decoded by receiver 38 (step 100). Mode data 54 instructs receiver 38 of the appropriate receiver mode for reception of data 48. Receiver 38 then adjusts to the appropriate receiver mode identified by mode data 54 (step 102). In one embodiment, the subsequent receiver modes (used to receive data 48) consume more energy. By enabling receiver 38 to detect and evaluate initial communications, and to receive channel and mode data, all prior to entering the high power communication mode, valuable energy savings are realized.

With receiver 38 now set to receive transmission bit stream 40 on the appropriate communication channel, and also configured to the appropriate receiver mode, transmitter 32 transmits data 48. Receiver 38 receives data 48 (step 102) and determines whether any further action is required. If data 48 contains a request for further communication, for example, receiver 38 passes that request to IMD circuitry 29 of IMD 12, which responds accordingly.

FIG. 10 is a timing diagram illustrating a second method of operating receiver 38, which includes operating in a wide band and a narrow band receiver mode. The diagram illustrates a repeating method of sampling for a transmission on the communication band. Each cycle around the circle represents a period of time, such as five seconds. Each cycle includes ten time slots, represented by T1-T10, each spaced by a shorter time interval, such as 0.5 seconds. The method progresses around the circle in a clockwise direction.

In a narrow band receiver mode, a transmission in the communication band is detected by sampling each channel individually, checking for energy present on that channel. Noise present in adjacent communication channels can be filtered out, resulting in improved receiver sensitivity. This is useful when transmitter 32 is a long distance away from receiver 38 (resulting in a very weak transmission signal) or in a noisy environment, and also for higher speed communication over any distance.

However, sampling each channel individually results in a decreased response time of the receiver and/or increased power consumption. For example, if the communication band includes ten individual channels, ten samples would be needed to check each channel for a communication. Furthermore, a communication present on one channel will only be detected when receiver 38 is sampling that one channel, and not when receiver 38 is sampling any of the other nine channels.

In wide band receiver mode, detecting a transmission on one of the channels of a communication band is achieved by simultaneously sampling the entire band of ten channels with receiver 38. This method results in increased receiver response time and reduced energy consumption. Because only a single sample needs to be taken to detect a transmission, far fewer samples are required.

However, the wide band receiver mode is less sensitive than the narrow band receiver mode, because all noise in the communication band is received, including transmissions from other nearby devices and other noise sources. As a result, the wide band receiver mode is best suited for slower speed communications over short distances.

Because there are benefits to operating in a wide band receiver mode, and other benefits to operating in a narrow band receiver mode, this embodiment provides a method of operating receiver 38 in both receiver modes to sample for a transmission on a communication channel. For example, at T1, receiver 38 powers up in wide band receiver mode 110. As previously described, wide band receiver mode 110 enables receiver 38 to sample all channels of the communication band at once. If energy is detected, receiver 38 validates the signal and adjusts to the narrow band receiver mode to receive the communication, as described with reference to FIG. 9.

Since wide band receiver mode 110 is capable of detecting energy on any of the channels, it is also less sensitive than the narrow band receiver mode. If no energy is detected in wide band receiver mode 110, receiver 38 adjusts to narrow band receiver mode 112, which provides improved noise rejection and sensitivity over wide band receiver mode 110. At T1, narrow band receiver mode is centered on first communication channel CH1. Even though wide band receiver mode 110 did not detect energy on the band, the increased sensitivity of narrow band receiver mode 112 allows receiver 38 to detect a weaker transmission or to filter out the transmission from a noisy environment. If energy is detected that conforms to the appropriate modulation, receiver 38 receives the transmission. If no energy is detected, receiver 38 turns off until the next time interval at T2.

Receiver 38 repeats the process at T2 by first sampling in wide band receiver mode 110, and then in narrow band receiver mode 112. However, at T2 receiver 38 samples the second communication channel CH2, rather than the first communication channel. Receiver 38 continues in this manner around the timing diagram until all channels have been individually sampled. If no energy is detected, receiver 38 repeats the process from T1 to T10. Receiver 38 performs a sample of all communication channels every 0.5 seconds, and performs a sample of each individual communication channel every 5 seconds.

This method enables receiver 38 to provide fast response times for close range communications with wide band receiver mode 110, while also providing high sensitivity for further distance communications or in noisy environments with narrow band receiver mode 112.

In another embodiment, receiver 38 includes a wide band receiver in parallel with a narrow band receiver. In this embodiment, receiver 38 is capable of operating in both the wide band receiver mode and the narrow band receiver mode at the same time, thereby reducing the total on-time of the receiver.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. In particular, although the present invention has been described in the context of transmissions from an external device to an implantable medical device, it can also be implemented between implantable devices, between external units, or for transmissions from implantable medical devices to external units.

Although the present invention has been described with reference to preferred embodiments, workers skilled in the art will recognize that changes may be made in form and detail without departing from the spirit and scope of the invention. In particular, one skilled in the art will recognize that although the present invention has been described for transmissions from an external device to an implantable medical device, it could also be implemented between implantable devices, between external units, among a wireless network of implantable and external devices, or for transmissions from implantable medical devices to external units. In addition, other known types of data encoding could be used to perform the same functions as pulse width encoding and frequency shift encoding described above. 

1. A medical device for receiving a transmission including data, the medical device comprising: device circuitry controlling the operation of the medical device and processing data; and a receiver operating in a wide band receiver mode to detect transmission and receiving the data in a narrow band receiver mode.
 2. The medical device of claim 1, wherein the receiver, when operating in the wide band receiver mode, detects the transmission on any one of multiple communication channels; and wherein the receiver, when operating in the narrow band receiver mode, receives the transmission of data on a single channel.
 3. The medical device of claim 2, wherein the transmission further comprises embedded channel data, and the receiver decodes the embedded channel data and adjusts from the wide band receiver mode to the narrow band receiver mode at a channel identified by the channel data.
 4. The medical device of claim 1, wherein the receiver alternates between operating in the wide band receiver mode and operating in the narrow band receiver mode to detect the transmission.
 5. The medical device of claim 4, wherein the receiver detects the transmission while operating in the narrow band receiver mode.
 6. The medical device of claim 4, wherein the receiver turns off for a period of time after operating in the narrow band receiver mode.
 7. The medical device of claim 1, wherein the medical device is an implantable medical device.
 8. The medical device of claim 1, wherein the receiver, when operating in the wide band receiver mode, is configured to receive frequencies from 402 MHz to 405 MHz.
 9. The medical device of claim 1, wherein the receiver comprises a super regenerative receiver for operating in the wide band receiver mode.
 10. The medical device of claim 1, wherein the receiver receives only one channel when operating in the narrow band receiver mode.
 11. A method of operating a medical device having a receiver to receive a transmission including data, the method comprising: operating the receiver in a wide band receiver mode to detect a transmission; and adjusting the receiver to a narrow band receiver mode to receive the data.
 12. The method of claim 11, further comprising: decoding channel data embedded within the transmission that identifies a communication channel to be used for receiving data in the narrow band receiver mode.
 13. The method of claim 11, wherein detecting a transmission comprises: detecting energy that exceeds a threshold value; and verifying a modulation pattern of the transmission.
 14. The method of claim 12, further comprising: receiving channel data embedded within a preamble of the transmission, wherein adjustment of the receiver to the narrow band receiver mode is in response to the received channel data.
 15. The method of claim 11, and further comprising: alternating between the wide band receiver mode and a narrow band receiver mode to detect the transmission.
 16. The method of claim 15, and further comprising: turning off the receiver for a period of time after operating in the narrow band receiver mode.
 17. The method of claim 15, wherein each time the receiver is operated in the narrow band receiver mode, the receiver samples a different communication channel in a communication band.
 18. A communication system comprising: an external unit having a transmitter for transmitting a transmission signal having a modulation pattern and data; and an implantable medical device having a receiver for operating in a wide band receiver mode to detect the transmission signal and verify the modulation pattern, and for operating in a narrow band receiver mode to receive the data.
 19. The communication system of claim 18, wherein the receiver comprises a super regenerative receiver for operating in the wide band receiver mode.
 20. The communication system of claim 18, wherein the receiver alternates between the wide band receiver mode and the narrow band receiver mode. 